Bactericide/Disinfectant Solution:
Chlorine compound bactericides such as sodium hypochlorite, calcium hypochlorite, and sodium dichloroisocyanurate have been extensively used as bactericides/disinfectants in a wide range of environments. Of these, hypochlorites including sodium hypochlorite are in general use from the standpoints of cost and effect. However, many proposals have been made for attaining improvements in the bactericidal/disinfectant effect thereof which are required in various fields including the clinical field and the food industry (see, for example, JP-A-2001-253803, JP-A-2001-342496, and JP-A-2002-145710).
Usually, such bactericides/disinfectants are prepared by adding the respective ingredients for constituting the composition to water or by mixing aqueous solutions containing the respective ingredients.
Use of Electrolytic Water as Substitute:
However, the use of chlorine compound bactericides in large amounts arouses troubles. For example, in factories and retail stores where food materials are handled in large quantities, cleaning with a sodium hypochlorite solution having a concentration exceeding 100 ppm is conducted. This cleaning, however, is regarded as problematic because it not only spoils the flavors of the food materials but also arouses a hazard (increase in THM).
Mainly for the purpose of eliminating those problems, investigations have been diligently made on the usefulness of electrolytic water, i.e., water yielded by electrolysis, in the agricultural, food, clinical, and other fields. The substitution of electrolytic water or ozonized water is proceeding mainly in Japan. Electrical energy, which is a clean energy, can be utilized to synthesize hydrogen, oxygen, ozone, hydrogen peroxide, etc. through chemical reactions on electrode surfaces while regulating the reactions. It is known that oxidation reactions especially on the anode yield oxidizing agents effective in water treatments (effective chlorine and peroxides such as ozone) and further generate active species such as OH radicals in some cases (Kyōsansei Denkaisui No Kiso Chishiki (Fundamental Knowledge of Strongly Acidic Electrolytic Water), Ohm-sha, Ltd.).
Attention is being directed to the excellent bactericidal/disinfectant activity of electrolytic water, and investigations are being made on the use of the water in clinical activities and in the home. Examples of the uses thereof which are being investigated include the sterilization/disinfection of diseased parts, incised parts, percutaneous openings for stationary catheters, etc. and the sterilization/disinfection of domestic utensils or articles, such as kitchen utensils, baby articles, and furniture, and house equipments such as the toilet facilities and bathtub. Such electrolytic water is obtained by electrolyzing water (water to be electrolyzed) to which a solute that generates ions upon dissolution, e.g., sodium chloride, has been added optionally together with an acid for pH regulation.
Kinds of Electrolytic Water:
Besides being used as a food additive, electrolytic water is usable also in other applications. In an electrolytic cell containing water only, the following anode reaction proceeds to evolve oxygen according to formula (1). However, depending on the catalyst and electrolysis conditions, ozone is yielded according to formula (2) and ozonized water containing the ozone dissolved therein can be synthesized.2H2O═O2+4H++4e  (1)3H2O═O3+6H++6e  (2)
In the case where the water contains hydrochloric acid or chloride ions added thereto, hypochlorous acid is yielded according to formulae (3) and (4). In the case where the water contains sulfuric acid, the reaction represented by formula (5) proceeds to yield persulfuric acid.Cl−═Cl2+2e  (3)Cl2+H2O═HCl+HClO  (4)2SO42−═S2O82−+2e  (5)
When carbonate ions are present, the reaction represented by formula (6) proceeds to yield percarbonic acid.2CO32−═C2O62−+2e  (6)
Through cathode reactions, it is possible to synthesize hydrogenous water, which is water containing excess hydrogen dissolved therein, alkali ion water, and the like according to formulae (7) and (8).2H++2e═H2  (7)2H2O+2e═H2+2OH−  (8)
Furthermore, hydrogen peroxide or the like can also be synthesized.
As shown above, electrolytic water containing two or more peroxides can be produced with electrolytes suitably selected, besides the acid waters which have been approved as food additives.
Features of Electrolytic Water: (reference: Mizu No Tokusei To Atarashii RiyōGijutsu (Characteristics of Water And Novel Application Technology), 2004, NTS Inc.)
There are the following three kinds of electrolytic water which have been approved as food additives.
a) Weakly alkaline electrolytic hypochlorite water (additive name, electrolytic sodium hypochlorite water; 20-200 ppm; pH>7.5; yielded from 0.2-2% aqueous sodium chloride solution using no diaphragm)
b) Slightly acid electrolytic water (additive name, slightly acid hypochlorous acid water; 10-30 ppm; pH=5-6.5; yielded from 2-6% hydrochloric acid using no diaphragm)
c) Strongly acid electrolytic water (additive name, strongly acid hypochlorous acid water; 20-60 ppm; pH<2.7; yielded as anolyte water from 0.2% or lower aqueous sodium chloride solution in diaphragm type cell)
The acid waters among those kinds of electrolytic water have, for example, the following merits.
(1) The acid waters are superior in safety because THMs are less apt to generate under acid conditions.
(2) Resistant bacteria are less apt to generate and on-site management is easy.
(3) The waters can be used for treatment in combination with the alkaline electrolytic water.
(4) The waters can be utilized like tap water and impart no remaining odor to the hands or fingers.
(5) Use of the waters just before suffices (sterilization time is short).
In the conventional treatment with sodium hypochlorite solutions, use of this chemical having a concentration up to 200 ppm as a food additive has been approved. However, the chemical spoils the flavor and has a residual tendency. In contrast, the electrolytic water of those kinds has a high bactericidal effect even in a low concentration and is beneficial, although use thereof necessitates an initial investment in the apparatus.
Features of Ozonized Water:
The long-term use of hypochlorites has yielded bacteria resistant to these chemicals, and there is a doubt about the bactericidal effect thereof. On the other hand, ozonized water has been placed on food additive lists and has gained approval of FDA (Food and Drug Administrations) of U.S.A. (2001) for use as a bactericide in food storage/production steps. Ozonized water has already come into many practical uses for sterilization in food factories and the sterilization of foods themselves. Recently, attention is focused on the fact that ozonized water is equal or superior in effect to sterilizing waters heretofore in use also in clinical fields such as dermatology, ophthalmology, and dentistry and is effective in reducing the burden to be imposed on the living body.
Ozonized water has, for example, the following merits.
(1) The bactericidal effect of ozone (OH radicals) is based on the oxidative destruction of cell walls and this indiscriminate activity is thought not to generate resistant bacteria.
(2) Ozone does not have a residual tendency.
When ozonized water is used in combination with an oxidizing agent having a residual tendency (e.g., a hypochlorite, persulfate, or percarbonate) according to need, a more effective sterilization treatment is possible.
Conventional Process for Producing Ozonized Water:
Ozonized water has conventionally been produced generally with a discharge type ozone gas generator. Ozonized water having a concentration of several parts per million parts can be easily produced by the process, and is being utilized in the fields of water purification treatment and food cleaning. However, the apparatus has been unsuitable for use as a handy ozonized-water production apparatus having excellent instant-response characteristics and yielding high-concentration ozonized water, for the following reasons.
(1) The ozonized-water production necessitates two steps, i.e., first generating ozone as a gas and then dissolving the gas in water.
(2) The ozonized water has a lower concentration than that produced by the electrolytic process which will be described later and, hence, the water should be produced through high-pressure injection into water and dissolution therein.
(3) The power source for ozone generation has a high voltage and a high frequency, making it difficult to attain a size reduction.
(4) In the ozonized-water production apparatus based on a discharged, a certain time period (stand-by time of several minutes) is required for the ozone gas generation ability to become stable and it is difficult to instantaneously prepare ozonized water having a certain concentration.
Electrolytic Ozone Production Process:
The electrolytic process is inferior to the discharge process in electric power consumption rate. However, a feature of the electrolytic process resides in that high-concentration ozone gas and ozonized water can be easily obtained. The electrolytic process is hence in general use in special fields such as, e.g., the cleaning of electronic parts. Since a direct-current low-voltage power source is employed because of the principle of the process, the apparatus is excellent in instant-response characteristics and safety and is expected to be used as a small ozone gas generator or a small ozonized-water production apparatus. According to applications, a driving mode can be selected from battery driving, power-generator driving, and AC-DC conversion driving.
For efficiently generating ozone gas, it is indispensable to select a proper catalyst and electrolyte. Known electrode materials include noble metals such as platinum, α-lead dioxide, β-lead dioxide, glassy carbon impregnated with a fluorocarbon, and diamond. As an electrolyte, use has been made of an aqueous solution containing sulfuric acid, phosphoric acid, fluorinated groups, or the like. However, these electrolytes have poor handleability and are not in extensive use. A water electrolysis cell which employs a solid polymer electrolyte as a diaphragm and in which pure water is used as a raw material is easy to manage in that respect and is in general use (J. Electrochem. Soc., 132, 367 (1985)). When lead dioxide, which has been employed as a catalyst, is used, ozone gas having a concentration as high as 12% or above is obtained.
In the system called a direct synthesis system, the solution located around an electrode is caused to flow at a sufficient velocity to thereby take out the ozone as ozonized water before gasifying (JP-A-8-134677). Furthermore, in the case where raw water other than pure water is supplied to the electrolytic system, the activity of the noble-metal electrode catalyst itself is influenced by the quality of the water. Care should hence be given to the fact that electrolytic performances such as life and efficiency fluctuate. JP-A-9-268395 discloses that conductive diamond is useful as an electrode for producing functional water (containing ozone).
Development of Small Apparatus:
Portable or small electrolytic-water production/ejection apparatus have been proposed in order to more easily conduct sterilization/disinfection or the like in clinical activities or in the home (see patent documents 1 to 3). Such small apparatus may be extensively used for the deodorization, sterilization, or bleaching of indoor facilities, water-related facilities, tableware, garments, etc. in the home or for business purposes or for the sterilization or disinfection of the human body, e.g., the hands or fingers, etc.
Patent Document 1: JP-A-2000-79393
Patent Document 2: JP-A-2000-197889
Patent Document 3: JP-A-2001-276826
Besides those, the following are known: JPA-2004-129954 (apparatus having a device which generates power necessary for electrolysis); JP-A-2004-130263 (apparatus in which the proportion of the capacity of the piston to the volume, sectional area, etc. of the cell cylinder part is a specific value); JP-A-2004-130264 (apparatus in which raw water for electrolysis comprising a pH regulator, surfactant, chlorine compound, and water is used to obtain electrolytic water having a pH of 3-8.5); JP-A-2004-130265 (the electrolytic water according to JP-A-2004-130264 is used in a foamed state); JP-A-2004-130266 (the direction of voltage application to the electrodes is changed alternately); JP-A-2004-148108 (the voltage to be applied to the electrodes is variable); JP-A-2004-148109 (apparatus having electrodes in a suction passage); JP-A-2003-93479, JP-A-2003-266073, and JP-A-2002-346564 (separation type having a cylindrical electrode in a spraying part); and JP-A-2001-47048 (gun type prevented from being clogged during non-spraying period and equipped with a motor).
Known techniques intended to synthesize ozonized water include the following. JP-A-2000-169989 discloses a small electrolytic ozone generator which has a structure including an assembly composed of a solid cylindrical shaft and, wound on the shaft, a metal-gauze-like anode (platinum), an ion-exchange membrane, and a metal-gauze-like cathode and disposed in a water channel and in which the shaft has a thin groove formed therein. JPA-2001-198574 discloses a module for connection to piping which includes a solid cylindrical shaft and, fixed to the shaft, a porous anode, a solid polymer electrolyte (ion-exchange membrane), and a porous cathode and has a drain line capable of separately discharging the ozonized water to be synthesized at the anode and the hydrogen/hydrogen gas to be synthesized at the cathode. JP-A-2002-143851 discloses a method of water treatment with a double-pipe structure including a supporting cylindrical member having a through-hole and, wound on the cylindrical member, a cathode, a membrane, and an anode. In this method, hard-water components can be inhibited from depositing from tap water as raw water by passing a dilute aqueous solution of sodium chloride through the cylinder serving as a cathode chamber, and an ultraviolet treatment can also be conducted simultaneously. JP-A-2004-60010 and JP-A-2004-60011 disclose an ozonized-water production apparatus which is capable of separating a catholyte with an electrolytic cell equal to that described in JP-A-2000-169989 and of measuring the concentration of ozone with an electromotive-force measuring device disposed in the channel. JPA-2006-346203 discloses use of conductive diamond as an electrode and, in particular, discloses an electrolytic cell including a rod-form conductive-diamond electrode, a strip-form diaphragm member disposed around the electrode, and a wire-form counter electrode disposed on the diaphragm member. Furthermore, JP-A-2007-136356 discloses a structure including a cylindrical core member having grooves extending in the cylinder direction and, wound on the core member in the following order, a cathode, a membrane, and an anode.